Process for the continuous manufacture of viscose products



Patented Sept. 4, 1951 PROCESS FOR THE CONTINUOUS MANU- FACTURIE F'VISCOSE' PRODUCTS Robert Levison, Ede, and Barend Jan, Blomberg, Velp,Netherlands, assignors to American Enka Corporation, Enka, N. 0., acorporation of Delaware No Drawing. Application March 16, 1949, Serial,No. 81,844. In the Netherlands May 7, 1948 'The present inventionrelatesto a continuous process for manufacturing viscose products, and

more particularly to. a process in which freshly formed viscose threadsare aftertreated by passing a large number of such threads throughtreating zones or in parallel relationship and in a sub- ,stantiallylinear direction through successive ,treating baths'at such high speedsthat the treatment time in each individual zone or bath is only afewseconds.

When' manufacturing products from viscose,

ous aftertreatments for the purpose of obtaininggail end-productconsisting of pure, cellulose hydrate, which has been completely freedof residues formed during the decomposition of the viscose and freedfrom spinbath constituents and from sulphur and other impurities.

In manufacturing viscose rayon according to the discontinuous process inwhich the threads are coagulated and partially regenerated in thespinbath, the threads containing the acids and salts from thespinbathare collected on bobbins or in pots and thereafter allowed toremain for several hours so that complete regeneration of the cellulose,or better said, the decomposition of the xanthate is effected. Incertain cases, after the threads'have left the spinbath they aresubjected to further regeneration in a second bath containing sulphuricacid, and, if desired, sodium sulphate, and then collected on bobbins orin pots.

However, even in this case it is necessary to store the packages forsome time in order to assure complete decomposition of th xanthate.

After the packages have been stored for a sufiixcie'nt time, they arepressure and/or vacuum washed with water to remove the acid and saltsand thereafter desulphurized, and if necessary,

bleached, and finally dried; In this discontinuous process since thethreads have been completely "regenerated prior to washing,desulphurizing and bleaching, no problem existed with respect to thedesulphurizing and bleaching operation. The

threads were properly desulphurized and bleached to a pure whiteproduct. i

In the most widely used continuous system for the manufactureandaftertreatment of viscose threads, the threads are subjected to thevarious aftertreatments by passing them around thread-;storage,othread-advancing devices in a multi- 4 Claims. (Chm-54) 2plicity of convolutions. During their passage around the ,devices theyare subjected to the required treatments, such as, partia1decomposition, final decomposition, desulphurizing, bleaching anddrying. However, even in this type of continuous process the time factoris not critical because the individual treatment operations consume, forexample, from 40 seconds to one minute, which, if acid and washingtreatments are given, are sufficient to effect proper desulphurizationand bleaching.

In all of the known discontinuous processes, and the continuousprocesses with thread storage, during the preparation and aftertreatmentof threads spun from viscose the decomposition of the xanthate wasadvanced by the liquid carried along by the thread from the originalspinbath'; when the decomposition seemed insuflicient, complementaryacid baths wer employed; Since, in these processes, time was no factor,it was not discovered that the sodium sulphate used in the baths orformed. during the decomposition of the xanthate. had a disadvantageousefiect on the decomposition of the thread, and therefore e steps weretaken to remove the salts. As a matter of fact, it is well known thatfreshly spun threads which are only partially decomposed require acertain amount of salt in the acid baths to prevent turgor-action, whichis caused by swelling of the interior of the filaments to a greaterextent than the exterior because of a skinlike formation at the exteriorof the filaments. This turgescent swelling results in the threadsbursting open and sticking together upon subsequent treatment withwater. or dilute acid baths free of salt.

A more recently developed. continuous system for manufacturing rayonproducts is described and claimed in U. S. Patent No. 2,334,325, U. S.Patent No. 2,459,254, U. S. application Serial No. 18,408,,now U; S.Patent No. 2,539,980 and U. S.

application Serial No. 713,905, now U. S. Patent No. 2,513,057 (bothassigned to the same assignee as the present application), French PatentNo. 884,700 and Britain application Serial No. 9,912/47. This group ofpatents and applications relate to a high speed continuous process inwhich the threads are passed in parallel, linearly through successivetreating baths at high rates of speed, for example, from meters perminute to meters or more per minute. This type of continuous spinning isvery simple and considerably cheaper to install and maintain than thesystems involving the storage devices. However, one disadvantage of thissystem is that due to the lack of space in a rayonmanufactur tions.

generated, i. e., the xanthate is not remains in the finished productwhereby a yellow discoloration occurs. While it is necessary to have acertain amount of salt present during the decomposition, as soon as thedecomposition of the xanthate has reached an advanced state, the saltsshould be washed out, because the presence of salt will appreciablydelay further decomposition. of the last-remaining very'small amounts ofxanthate residues. 7

Primarilyit was determined that the principal .aftertreatments, viz.,complete decomposition of the xanthate and desulphurization aredependent on each other, in that, the desulphurizing proceeds morecompletely in direct relation to the degree of decomposition of thexanthate remaining in the threads. If the decomposition of the xanthateis not substantially complete or below a definite predetermined limitthen the desulphurizing operation cannot be performed properly, i. e.,all of the sulphur cannot be removed in the time allotted and thisresidual sulphur will show up in the final product which will lowerthequality thereof. Onv the other hand, as soon as the decomposition ofthe xanthate has reached a very advanced stage, e. g., the xanthateratio. falls-below .003 or preferably below .002, the desulphurizationcan be carried out in a reliable manner that is completely satisfactoryfor all practical purposes. Prior to the present invention when usingone of the normal desulphurizing agents such as sodium sulphide, it hasnotbeen possible to remove all of the sulphur in a continuous processinvolving high speed treating. operations. Because of this, continuousspinning of this type has not been practical, and has therefore beenslow in its commercial development.

v It is therefore-the object of the present invention. to provide aparticular type of aftertreatment or series of aftertreatments that canbe utilized effectively in this more recently developedcontinuousspinning system.

Another object, of the invention is to decompose the residual xanthatein. the freshly spun threads-in several seconds but so completely thatthe threads can be immediately desulphurized so thoroughly within; avery few seconds that nosulphurdeposits can be detected in the finalproduct. V u

A still-further object of the invention is to employ certain materialsin: the: aftertreatment baths that will accelerate the decomposition ofthe last remaining xanthate in the threads to quickly lower thexanthateratio below a critical point, i. e., below .003 or .002.(The'xanthate ratio, i. e., the ratio of the number of residual xanthategroups to the total number of cellulose groups (CsHmOsJ' is'determinedby any of the well known chemical methods. One suit able determinativemethod is described in Leroy H; Smith, Synthetic Fiber Developments inGermany 1946, pages 201-204.)

Other objects and advantages of the invention will become apparent fromthe following detailed description.

In practicing according to the present invention and utilizing high.spinning speedsin which individual treatments are effected in less than10 seconds, it was first determined that after the thread has beencoagulated and partially regenerated in a normal sulphuric acid,salt-containing spinbath, the further decomposition of the xanthate "canbe effectively accomplished by meansof a ,hot dilute acid bathcontaining sulphuric acid in a range of 0.5%6.0% and correspondingly1.0% to 10% sodium sulphate, said bath being vmaintained at atemperature in the range of 60 to 95 C.

Bypassing the thread through such a hot dilute acid bath, it can besubstantially completely regenerated in three or four seconds, althougha small amount of residual undecomposed xanthate (X. R. about 0.02) doesremain in. the

thread which must be removed prior. to desulphurization. It has beendetermined that the remaining amount of undecomposed xanthate can beremoved or the xanthate ratio can be reduced below .003 in 3 or 4seconds, after a thorough washing to remove the salts from the thread,by immediately passing the thread through a pure dilute sulphuric acidbath (not diluted spinbath) containing sodium. sulphate substantiallybelow the bisulphate raltio,.i. e., for every mol of. sulphuric acid,less than 1 mol of sodium sulphate is used. This means thatthe molecularratio of sodium sulphate to sulphuric acid is substantially less than1:1. Therefore, it is necessary, for example, when using 3% sulphuricacid to take precautions thatthe salt content can never be as muchas'4.3% sodium sulphate. Particularly good results have been achievedwhen using 4% sulphuric acid and 2% or less sodium sulphate, whichcorresponds to a molecularratio of 2.8:1. In this way thesalt contentcan always be maintained at a predetermined value below the bisulphateratio because the threads being first washed and then treated witha'pure sulphuric acid bath as distinguished from a dilute spinba-th, thesalt content can never increase asin the casewhere thethread containingsalts is allowed to pass through the treatment bath wherein the saltcontent continually builds up.

Asan alternative procedure for treating'the thread in a dilute sulphuricacid bath containing sodium sulphate below the bisulphate ratio for thepurpose of removing the remaining amount of undecomposed xanthate, thethread can be treated in a bath containing certain oxidizing decomposingagents, such as H202, KzSzOa, H0103, HC1O4, NaOCl, NaClO2, NaNOz. Dilutesolutions .of-sodium hypochlorite or sodium chlorite were found tobeparticularly ellective. When using solutions of sodium hypochlorite,the best concentration range is between 0.5% and 2%, and the solutionismaintained at room temperature. When using sodium chlorite, preferablyin acid solutions, the best results are attained at a highertemperature, for example 70 0. although the bath having an acidconcentration of from 0.5% to 6% and sodium sulphate in a concentrationof 1.0% to 10%, said bath being maintained at a temperature of from 60to 95 C., or the threads are subjected to further regeneration by thespin bath liquid retained in the threads, but in either case thexanthate ratio can only be lowered to about 0.02 which is insufficientto effect complete desulphurization in the time available. The threadsare then washed with water or other suitable treating liquid to removethe salts therefrom. Next the threads are passed through a dilute puresulphuric acid bath containing sodium sulphate below the bisulphateratio or through a bath containing an oxidizing agent. This treatmentlowers the xanthate ratio below the critical point, namely, below .002or at least below .003. The thus treated threads are again washed bypassing them through a water bath, and are then immediatelydesul'phurized and bleached in suc cessive baths, and finally dried.This process is a continuous one from the beginning to the end, and eachof the treatment operations are effected in 3 or 4 seconds, or less, butin any case, never more than 10 seconds.

The invention is not limited to normal rayon such as 2.5 and 5 filamentdenier, but is also applicable to the preparation of thicker productsmade from viscose such as horsehair, ribbons, and films, and when theexpression threads is used in the claims it is intended to cover theseother said products.

Obviously, various modifications may be made without departing from thespirit and scope of the invention, e. g., it may not be necessary toutilize the washing step between the last decornposing bath and thedesulphurizing bath, pro= vided some equivalent means is used to removethe acid such as by an expressing operation.

What is claimed is:

1. A process for the continuous manufacture of viscose threads whichcomprises extruding a multiplicity of threads through spinnerets into acoagulating bath containing sulphuric acid and salts thereof, passingthe threads in parallel relationship linearly through a second bath atsuch a high speed that the time of passage through the bath is less thanten seconds thereby lowering the xanthate ratio to about 0.02, which isinsufficient to permit subsequent complete desulphurization, said secondbath being maintained at a temperature in the range of 60 C.-95 C. andcontaining a lower concentration of acid and salt thanthat of the firstbath, washing the threads free of salts, decomposing the remainingxanthate in the threads to a xanthate ratio below 0.003 by treating themin a solution containing sulphuric acid and sodium sulphate below thebisulphate ratio, and again washing the threads and effectingsubstantially complete desulphurization, each of said treatments beingeffected in less than ten seconds.

2. A process for the continuous manufacture of viscose threads whichcomprises extruding a multiplicity of threads through spinnerets into acoagulating bath containing sulphuric acid and salts thereof, passingthe threads in parallel relationship linearly through a second bath atsuch a high speed that the time of passage through the bath is less thanten seconds thereby lower ing the xanthate ratio to about 0.02, which isinsufficient to permit subsequent complete desulphurization, said secondbath being maintained at a temperature in the range of 60 6-95" C. andcontaining a lower concentration of acid and salt than that of the firstbath, washing the threads free of salts, decomposing the remain ingxanthate in the threads to a Xanthate ratio below 0.003 by treating themin a solution con taining sulphuric acid in a concentration of 0.5%-6.0% and sodium sulphate below the bisulphate ratio, and again washingthe threads and eflecting substantially complete desulphurization, eachof said treatments being effected in less than ten seconds.

3. A process for the continuous manufacture of viscose threads whichcomprises extruding a multiplicity of threads through spinnerets into acoagulating bath containing sulphuric acid and salts thereof, passingthe threads in parallel relationship linearly through a second bath atsuch a high speed that the time of passage through the bath is less thanten seconds thereby lowering the xanthate ratio to about 0.02, whichinsuiiicient to permit subsequent complete desulphunization, said secondbath being maintained at a temperature in the range of 60 0-95" C. andcontaining a lower concentration of acid and salt than that of the firstbath, washing the threads free of salts, decomposing the remainingxanthate in the threads to a xanthate ratio below 0.003 by treating themin a solution containing about 4.0% sulphuric acid and less than 2.0%sodium sulphate, and again washing the threads effecting substantiallycomplete desulphurization, each of said treatments being affected inless than ten seconds.

4. A process for the continuous manufacture of viscose threads whichcomprises extruding a multiplicity of threads through spinnerets into acoagulating bath containing sulphuric acid and salts thereof, passingthe threads in parallel relationship linearly through a second bath atsuch a high speed that the time of passage through the bath is aboutthree or four seconds thereby lowering the xanthate ratio to about 9.02,which is insufficient to permit subsequent complete desulphurization,said second bath being maintained at a temperature in the range of 60C.- C. and containing a lower concentration of acid and salt than thatof the first bath, washing the threads free of salts, decomposing theremaining xanthate in the threads to a xanthate ratio below 0.003 bytreating them in a solution containing sulphuric acid and sodiumsulphate below the bisulphate ratio, and again washing the threads andeffecting substantially complete desulphurization, each of saidtreatments being effected in about three or four seconds.

ROBERT LEVISON. BARE-ND JAN BLONIBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,915,952 Richter et al June 27,1933 2,309,072 Burkholder Jan. 19, 1943 2,427,993 McLellan Sept. 23,1947

1. A PROCESS FOR THE CONTINUOUS MANUFACTURE OF VISCOSE THREADS WHICHCOMPRISES EXTRUDING A MULTIPLICITY OF THREADS THROUGH SPINNERETS INTO ACOAGULATING BATH CONTAINING SULPHURIC ACID AND SALTS THEREOF, PASSINGTHE THREADS IN PARALLEL RELATIONSHIP LINEARLY THROUGH A SECOND BATH ATSUCH A HIGH SPEED THAT THE TIME OF PASSAGE THROUGH THE BATH IS LESS THANTEN SECONDS THEREBY LOWERING THE XANTHATE RATIO TO ABOUT 0.02, WHICH ISINSUFFICIENT TO PERMIT SUBSEQUENT COMPLETE DESULPHURIZATION, SAID SECONDBATH BEING MAINTAINED AT A TEMPERATURE IN THE RANGE OF 60* C.-95* C. ANDCONTAINING A LOWER CONCENTRATION OF ACID AND SALTS THAN THAT OF THEFIRST BATH, WASHING THE THREADS FREE OF SALTS, DECOMPOSING THE REMAININGXANTHATE IN THE THREADS TO A XANTHATE RATIO BELOW 0.003 BY TREATING THEMIN A SOLUTION CONTAINING SULPHURIC ACID AND SODIUM SULPHATE BELOW THEBISULPHATE RATIO, AND AGAIN WASHING THE THREADS AND EFFECTINGSUBSTANTIALLY COMPLETE DESULPHURIZATION, EACH OF SAID TREATMENTS BEINGEFFECTED IN LESS THAN TEN SECONDS.